1. Technical Field
The present invention relates generally to electrical circuits and in particular to transformer circuits. Still more particularly, the present invention relates to multiple winding transformer circuits and designs and applications thereof.
2. Description of the Related Art
Variable frequency drives are generally used to control the frequency of the electrical power supplied to an alternating current (AC) motor system. One use of variable frequency drives is to power large pumping systems in the offshore petroleum industry. Different types of variable frequency drives exist, with one type being made up of multiple three-phase to single-phase converters/inverters. Each of the multiple converters/inverters is electrically isolated from the others. The multiple converters/inverters are then connected in three series circuits to compose three output phases of the variable frequency drive. FIG. 1 illustrates an example variable frequency drive 100 with three output legs, output A, output B, and output C, each comprised of four series-connected three-phase to single-phase converter/inverters 110. The legs of the variable frequency drive are connected at a midpoint neutral 107. Powering of these types of variable frequency drives (100) requires the use of one or multiple three phase power supply system(s) or power source(s), and this three phase powering is difficult because of the complexity of the variable frequency drive (e.g., multiple isolated three phase inputs are required for the converters/inverters). Additionally, with these variable frequency drives and the conventional powering systems applied/utilized, the overall configuration/design manifests/exhibits a high incidence of harmonic currents in the power supply. Also, the conventional configuration/design manifests/exhibits the presence of transient voltages, which are induced into the output circuits.